M theory is a name for a more unified theory that has the different string theories, as we know them, as limits, and which also can reduce, under appropriate conditions, to eleven-dimensional supergravity. There's this picture that we all have to draw where different string theories are limits of this M theory, where M stands for Magic, Mystery or Matrix, but it also sometimes is seen as standing for Murky, because the truth about M theory is Murky. And the different limits, where the main parameter simplifies, give the different string theories -- Type IIA, Type IIB, Type I, and there's eleven-dimensional supergravity, which turns out to be an important limit even though it isn't part of the systematic perturbation expansion, then there's the E8XE8 heterotic string, and there's SO(32) heterotic string. So M-theory is a name for this picture, this more general picture that will generate the different limits through the different string theories. The parameters in this picture we can think of being roughly hbar, which is Planck's constant, and that determines how important the quantum effects are, and the other parameter is alpha prime, which is the tension, related to the tension of the string, that determines how important stringy effects are. So traditionally, a physicist looking at Type IIA, for example, by traditional weak coupling methods, explores this little region, and if asked how his theory is related to Type I theory, the answer would have to be, "Well I don't know, that's something else." And likewise, if you ask this observer what happens for strong coupling, the traditional answer was, "Well I don't know." In graduate courses, you learn that you can do more or less anything for weak coupling, but you can't do anything for strong coupling. What happened in the 90s was that we learned how to do a little bit for strong coupling, and it turned out that the answer is Type IIA at strong coupling turns out to be Type I in a slightly different limit, SO(32) heterotic, and so on. So we built up this more unified picture, but we still don't understand what it means

Dr. Ed Witten, Princeton University

My favorite passage from Dr. Witten's statement:

And the different limits, where the main parameter simplifies, give the different string theories -- Type IIA, Type IIB, Type I, and there's eleven-dimensional supergravity, which turns out to be an important limit even though it isn't part of the systematic perturbation expansion

My second favorite passage:

...but we still don't understand what it means

William

Last edited by William on Thu Mar 24, 2005 5:54 pm, edited 2 times in total.

My apologies, BD, to you and to the rest of the Agorans. Dr. Witten, a physicist, is widely believed to be the most intelligent man in the world, even smarter than Albert Einstein and Steven Hawking, and I don't dispute that. I certainly lack the knowledge and no doubt the native intellegence to do so.

This was undoubtedly the wrong forum to post this. But I found his statement on string theory to be very amusing and his use of English interesting. I wondered if he didn't have his tongue in his cheek when making the quoted statement.

I think I'm in the wrong class! Isn't this Philosophy of Language 401?

This stuff does sound like non-sense, or semi-sense, to people outside the field of physics, but, as in any field, the words that we recognize are not so trustworthy; they have been differentiated into special meanings and denotations which results in a special set of words called a jargon.

Are strings really strings?

Of course, "I don't know" is a technical term in any jargon.

Apo

'Experiments are the only means of knowledge at our disposal. The rest is poetry, imagination.' -Max Planck

This stuff does sound like non-sense, or semi-sense, to people outside the field of physics, but, as in any field, the words that we recognize are not so trustworthy; they have been differentiated into special meanings and denotations which results in a special set of words called a jargon.

Yes, I understand about Jargon. At first I thought I might have uncovered Buzz'z true identity but Dr. Witten hasn't once referred to nahuatl in any of his stuff that I have seen, so I have to conclude that he's probably not buzz, although I still suspect Dr. Witten of having a sense of humor of some sort.

William, thanks for starting this thread. This is one of the truly neat things about the Internet, that you can share information so easily. I might not find myself reading across this type of stuff except for the efforts of cyber-friends.

I admit that I had never heard of Dr. Witten until the other night while watching NOVA on PBS. The program was entitled "The Elegant Universe". I think you can get a copy from CBS for about a hunderd bucks or so. Anyway, I am fascinated by many things myself, especially the Universe, though I lack the intellect for math necessary to understand most of what most astronomers and physicists are talking about. I am also fascinated by scientists, and have had a lot of fun learning about some of them over the years.

At first I thought I might have uncovered Buzz'z true identity but Dr. Witten hasn't once referred to nahuatl in any of his stuff that I have seen, so I have to conclude that he's probably not buzz, although I still suspect Dr. Witten of having a sense of humor of some sort.

Dr. Witten:

There's this picture that we all have to draw where different string theories are limits of this M theory, where M stands for Magic, Mystery or Matrix, but it also sometimes is seen as standing for Murky, because the truth about M theory is Murky.

I think this is a true joke, a dry one, but a joke none the less. The problem is that I don't have any audio or gestural cues to tell for sure.

I was trying to say that since string theory and the terms of physics are somewhat foreign to me, what I find funny might be very different from what another physicist or student of physics would find funny! And what they might take as funny might make perfect humorless sense to me.

After a few lectures or audio/videos I am sure I would catch on to his sense of humor or lack there of.

Apo

'Experiments are the only means of knowledge at our disposal. The rest is poetry, imagination.' -Max Planck

William, are you familiar with Michael Talbot's work? The Holographic Universe has showcases his views on life, the universe, and everything. gailr

gailr, I have not heard of the Holographic Universe nor of Michael Talbot. Thank you for the tip, though. I will look for it on the internet. I assume "The Holographic Universe" is a book title. If so, Amazon probably has it.

I did go to the link and it reminded me of a quote in a book I bought 15 years ago or so, "The Astronomers' Universe" by Herbert Friedman, a past direcor of the Space Science Program at the Naval Research Laboratory. I looked for the quote in the book but it looks like I'm going to have to read the book again to find it. Anyway, Friedman quotes an astronomer who said, "science is often wrong, but never in doubt".

An example of the old guard not accepting new ideas, Sir Arthur Eddington, who held the "plumian chair of astronomy" at Cambridge University led the expedition to South America in 1919 that discovered during a solar eclipse, that light really is affected by gravity, thus supporting Einstein's General Theory of Relativity. Eddington was a fairly young astrophysist at the time. Later, in the 1930s, Edington rejected Subrahmanyan Chandrasekhar's (a young student from India) equations that indicated that stars greater than 1.4 solar masses would, at the end of their lives, collapse to "incredibly dense objects", i.e. neutron stars and black holes. Eddington called Chandrasekhar's theory absurd, but "Chandrasekhar's Limit" was later proven to be correct. In 1984 Chandrasekhar shared the Nobel Prize in physics with another scientist. Chandrasekhar died only a few years ago.

Horses probably don't attend human foot races because, why would they waste their time watching animals who are so much slower than horses race against each other.

The following story recounts an amusing incident from the history of the west that exemplifies what happens when a man tries to race a horse, and what happens to a man's intelligence when his brain is saturated with alcohol.

By 1878, George Warren was living in the camp that was to become Bisbee, where there was a group of rough cabins at the confluence of Brewery Gulch and Tombstone Canyon. He had sold some claims, but held on to a 1/9 interest in the Copper Queen claim that had been given to him by a partner.

Here again the stories vary, but the basic line is that George got drunk and bet his interest in the Copper queen that he could outrun a horse. The famous event took place in Charleston, on the San Pedro River southwest of Tombstone.

The race was to be over a distance of 100 yards, including a turn around a post for the final leg homeward. Warren’s fuzzy reasoning was that he could take the turn much quicker than the horse and make up what he lost in the straightaway. Such "reasoning" came after "friends" made sure he had plenty of liquid refreshment. He was right about the turn, but wrong about the distance. In short, the horse ate his lunch.

In hindsight, it’s easy for us to know that Warren’s claims ended up being worth big bucks. Warren didn’t know what the value was, so it’s not as if he wagered, say, $1 million on a horse race. A claim he sold earlier brought him only $800, and that’s reasonable amount for a man to bet on a race. And if he had won, he would have gotten himself a fine horse — the one that beat him.